Realtime jitter, noise and eye-diagram analysis

DPOJET is the premiere eye-diagram, jitter, noise, and timing analysis package available for real-time oscilloscopes. Operating in the Tektronix DPO/DSA/MSO70000, DPO7000, and MSO/DPO5000 Series oscilloscopes, DPOJET provides engineers the highest sensitivity and accuracy available in real-time instruments. With comprehensive jitter and eye-diagram analysis and decomposition algorithms DPOJET simplifies discovering signal integrity concerns and jitter and their related sources in today's high-speed serial, digital, and communication system designs.

Analog and digital designers in the computer, semiconductor, and communications industries are facing new challenges as processor clock speeds race beyond 3 GHz and back-plane bus and serial link data rates exceed 8 GT/s. These increasing speeds mean reduced circuit tolerance, or margin, for jitter and related signal integrity problems. By using tools that help you rapidly characterize and discover sources of jitter and signal integrity concerns, you can bring new designs to market faster, with more confidence that they operate reliably in today's ultra high-speed environment.

DPOJET Jitter and Eye-diagram Analysis Tools extend the capability of Tektronix real-time oscilloscopes, performing complex measurements and analysis of clock, serial, and parallel data signals captured in Single-shot Acquisition mode or in Continuous-run Acquisition mode. Measurements in DPOJET are supported on either analog or digital channels as shown in the measurement table. Providing jitter and timing measurements with pass/fail parameter testing, and eye diagrams with mask testing for today’s most common industry standards, DPOJET is specifically designed to meet the advanced measurement needs of today's high-speed digital designers in the computer and communications industries.

As data rates increase, next generation interfaces present new test and measurement challenges, including the need to measure and isolate sources of BUJ (for example crosstalk). Crosstalk can be caused due to the coupling of energy on the lane under test from adjacent lanes.

While Receiver and Transmitter Equalization can compensate for data dependent jitter (DDJ), crosstalk effects are difficult to remove. This has resulted in many standards, for example Thunderbolt, including BUJ in the jitter budget making BUJ a required measurement.

When using the BUJ Jitter Decomposition method, the NPJ measurement is available in the Jitter tab within DPOJET.

Noise analysis with DPOJET (Opt. DJAN)

In the past, users have relied on jitter measurements and visualization to understand the behavior of their device under test. The test methodologies defined by many of the standard bodies have largely been concerned with the impact of jitter on horizontal eye closure. As data rates increase, the eye that is being analyzed has become smaller and smaller, making analysis of both vertical and horizontal eye closure a requirement. Understanding both the impact of jitter and noise enables engineers to predict the overall eye opening at a target bit error ratio. Traditional jitter and noise measurements provide analysis at a single sampling point, a BER contour can show much more about the overall behavior of a system. In the plot below, the user can quickly visualize the eye opening at many different target bit error ratios. As expected the more vertical closure as the BER increases, the more random noise is in the system. The same is true for random jitter in the horizontal direction.

Jitter and Noise bathtub plots are also useful in visualizing the effects of jitter and noise on eye closure. These plots represent a single sampling point as configured in the jitter and noise measurements.

With the reliance on transmitter and receiver equalization in many of today's high speed serial standards, it is also useful to visualize the effects of the equalization on the eye diagram. Equalization is good at compensating for data dependent jitter that may be caused due to the effects of the channel. When observing an acquired eye diagram, the eye diagram is composed of the entire population in the acquisition. This can make it difficult to visualize the composition of the eye due to data dependent jitter.

The eye diagrams below illustrate the correlated eye of a signal before a channel, after a channel, and after equalization. We expect that the correlated eye will have more eye closure after the channel and that the correlated eye width after the equalization would closely match the acquired eye width prior to the channel if the equalizer is effectively compensating for the data dependent jitter. In this case the eye widths are within ~3ps as shown in the eye diagram on the left and right hand sides.

Debug, Characterization, and Compliance

DPOJET is the only Jitter, Noise and Eye Analysis software that enables multi-source analysis with configuration flexibility on a measurement by measurement basis providing the ultimate debug, characterization, and compliance environment.

Multi-Lane Analysis

With other jitter, noise and eye analysis software solutions, analyzing multiple lanes is a painstaking process requiring multiple acquisitions to analyze each lane individually. DPOJET provides the capability to perform multiple measurements simultaneously on multiple sources, for example Ch1, Ch2, Ch3, and Ch4 enabling multi-lane analysis. Multiple lanes of traffic can be measured simultaneously allowing faster analysis and easy comparison of results for multi-lane standards including PCI Express, HDMI, and DisplayPort. This makes it easy to do visual comparison between the lanes and quickly note differences in signal quality parameters, for example noise, jitter, rise time, fall time, and amplitude between the lanes. Also available is DPOJET Reports which allows the generation of a html report which contains instrument and measurement configuration details, measurement results, and plots.

Simultaneous analysis of a four lane DisplayPort device.

Multi-Source Analysis

Building upon the ability to perform the same measurement simultaneously multiple times, DPOJET provides an environment that is well suited for analyzing the effects of post-processing actions, for example de-embedding, embedding, and equalization. Together with SDLA Visualizer, DPOJET provides the analysis environment which allows simultaneous measurements on the signal and different test points within the link. For example, a comparison between the acquired waveform and the waveform after de-embedding can be quickly done providing the details needed to validate the effects of de-embedding on the acquired signal.

Analysis of a PCI Express Gen 3 signal after channel embedding, CTLE, and DFE using SDLA Visualizer and DPOJET.

Multi-Measurement Configuration

Most high speed serial standards specify a reference phased locked loop (PLL) to use for clock recovery. This ensures that during the testing process that devices are all tested to the same standard. These PLLs are defined to filter or track the effects of low frequency jitter such as jitter due to Spread Spectrum Clocking (SSC). When using a PLL configuration that can track SSC, the SSC is attenuated and the result is a more open eye diagram. Typically, a 2nd order PLL is used to track the effects of SSC due to the ability to attenuate low frequency jitter. In cases where it is desired to see the effects of SSC constant clock recovery can be used which will not track the effects of SSC. Oftentimes, it is desired to see the effects of jitter, like SSC while at the same time evaluating the eye after using the reference PLL. This can quickly be done using the flexible measurement configuration feature in DPOJET. Measurements can be configured to all use the same clock recovery technique or individual measurements can be configured using different clock recovery methods.

In other cases, it is desired to see the results in the frequency domain. DPOJET provides a spectral plot which shows the spectral content of the signal after clock recovery. The spectral content of the signal can quickly be compared after applying a 2nd order pll versus using constant clock recovery as shown in the image above.

Data Visualization

DPOJET supports displaying measurement results and plots on the internal display, on an external monitor, or both locations, thus making full use of the oscilloscope dual display ports.

DPOJET provides a rich set of interactive plots that enable analysis beyond what is possible with static plot images. Interactive features include zoom, pan, cursors, and finding the min and max values. For example, when looking at the spectral plot it is easy to find the frequency with the highest amplitude by using the Max cursor feature. The plot readout will then show the frequency and the amplitude of jitter.

DPOJET analysis plots, like Spectrum and Trend, go beyond simple measurements and results display. Trend analysis quickly shows engineers how timing parameters change over time, like frequency drift, PLL startup transients, or a circuit’s response to power supply changes. Spectrum analysis quickly shows the precise frequency and amplitude of jitter and modulation sources for easy, rapid identification. Finding sources like adjacent oscillators and clocks, power supply noise, or signal crosstalk is no longer a tedious chore. Unique in the industry, DPOJET also provides Phase Noise plots to show jitter in root/Hertz and Transfer Function plots that allow direct comparison of jitter spectrums between two signals of differing frequencies, providing the perfect tool for determining jitter in PLL circuits like clock multipliers. The composite histogram plot shows further details into the jitter components and their distribution in the data set.

Composite histogram plot.

DPOJET Spectral Plots showing the effects on different clock recovery schemes on the amplitude of low frequency jitter.

Once all measurements are completed, the user has the flexibility to generate a test report which includes the instrument configuration, probe configuration, measurement results with pass fail status, measurement configuration details, and any plots that were generated. Alternatively, the user also has the flexibility to generate a .csv file that contains the results.

Example DPOJET Test Report showing measurement results and plots.

Ordering information

Model

DPOJET Jitter Analysis and DPOJET Noise Analysis

Options

Opt. DJA

Order preinstalled on a new oscilloscope

Opt. DJAN

Order preinstalled on a new oscilloscope, requires option DJA

Upgrades

Order an upgrade for existing oscilloscope:

DPO-UP Opt. DJAE

MSO/DPO5000 Series

DPO-UP Opt. DJAM

DPO7000 Series

DPO-UP Opt. DJAH

DPO/MSO70000 Series, 4-8 GHz

DPO-UP Opt. DJAN

DPO/MSO70000, DPO7000, MSO/DPO5000 Series

DPO-UP Opt. DJAU

DPO/MSO70000 Series, >12 GHz

DPOFL-DJA

Floating License

DPOFL-DJAN

Floating License, requires option DJA

Physical characteristics

Software is supplied on internal hard disk and on compact disk media, or can be downloaded from www.tektronix.com. Software installs and operates with DPO/DSA/MSO70000, DPO7000, or MSO/DPO5000 Series oscilloscopes. Online documentation and printable manual in PDF format are supplied with the product.

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